1. Field of the Invention
The present invention relates to a solar radiation sensor for being mounted on a motor vehicle for detecting the quantity of solar radiation incident upon the passenger compartment of the motor vehicle.
2. Description of the Prior Art
One example of solar radiation sensor of the type concerned is disclosed in Japanese Patent Laid-open Publication No. 58-19484, which includes a case, a filter fixed to an upper surface of the case, and a photodetector for detecting the quantity of solar radiation coming through the filter.
Since a light-receiving surface (sensing surface) of the photodetector is so arranged to face vertically upwards when the solar radiation sensor is set on a flat surface, the photodetector is hardly possible to catch or sense the solar radiation when the altitude of the sun is low. Consequently, a desired directivity is difficult to obtain when the solar radiation comes from a particular direction at a large incident angle.
In addition, the filter has a flat surface and hence the light-collecting efficiency of this filter is low.